Suspicious HTML File Creationedit

Identifies the execution of a browser process to open an HTML file with high entropy and size. Adversaries may smuggle data and files past content filters by hiding malicious payloads inside of seemingly benign HTML files.

Rule type: eql

Rule indices:


Severity: medium

Risk score: 47

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100


  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Initial Access

Version: 100 (version history)

Added (Elastic Stack release): 8.4.0

Last modified (Elastic Stack release): 8.5.0

Rule authors: Elastic

Rule license: Elastic License v2

Investigation guideedit

Rule queryedit

sequence by with maxspan=5m [file where event.action in
("creation", "rename") and file.extension : ("htm", "html") and
file.path : ("?:\\Users\\*\\Downloads\\*",
"?:\\Users\\*\\AppData\\Local\\Temp\\Rar$*") and ((file.Ext.entropy
>= 5 and file.size >= 150000) or file.size >= 1000000)] [process
where event.action == "start" and ( ( in
("chrome.exe", "msedge.exe", "brave.exe", "whale.exe", "browser.exe",
"dragon.exe", "vivaldi.exe", "opera.exe") and process.args == "--
single-argument") or ( == "iexplore.exe" and
process.args_count == 2) or ( in ("firefox.exe",
"waterfox.exe") and process.args == "-url") ) and process.args :

Threat mappingedit


Rule version historyedit

Version 100 (8.5.0 release)
  • Formatting only